quak files COLLECTION fetches that collection's files alone (closes #217)

`quak files COLLECTION` used to wait for a full refresh, which on an
empty cache fetched the files of every collection first. It now reads
the collection list, then calls the new `Library.refreshCollection()`.
That brings one collection up to date in the store as a refresh would.
Once the stored cursor is past 0, it only updates a collection the store
holds. For a new one, `quak files COLLECTION` waits for a refresh. A
refresh from a cursor of 0 replaces all the store holds, so collections
keep the server's order. `open()` awaits the first refresh while the
cursor is 0. The store lists what did not decrypt in a fixed order.

Model: opus-5-5

README.md

@@ -2,21 +2,31 @@
 
 quak is a WTFPL-licensed TypeScript client library and CLI by
 [@sneak](https://sneak.berlin) for the [Ente](https://ente.io) end-to-end
-encrypted photo hosting service. It logs in, enumerates collections and files,
+encrypted photo hosting service. It logs in, lists collections and their files,
-and downloads individual images while decrypting them on the way to disk.
+and downloads and decrypts single files.
 
-quak also includes a resilient backup command that downloads every file in the
+`quak backup` downloads every file in the account into a local directory tree.
-account into a deduplicated local directory tree, skipping files that already
+It downloads and stores each file once, however many collections hold it. It
-exist on disk and continuing past individual download failures instead of
+skips files already on disk. It logs a failed download and moves on to the next
-crashing. For each file it persists the basic metadata fields quak keeps (title,
+file. Beside each file it writes a JSON file that holds:
-file type, creation and modification time, latitude, longitude, content hash),
+
-its update time, and the private and public magic metadata in full. It keeps any
+- the file's title and file type
-ML data Ente has for the file, except the CLIP embedding, and writes the file's
+- its creation and modification times
-keywords in place of the embedding. For an image (for a live photo, its image),
+- its latitude and longitude
-it keeps its original's EXIF and XMP, with its dimensions for a JPEG only. For a
+- its content hash
-video it keeps none of these three. It runs unattended from cron (see "Running
+- its update time
-the backup from cron"). A helper subcommand can detect and regenerate missing
+- its private and public magic metadata, in full
-thumbnails, encrypting and uploading them back to the server.
+- the ML data that Ente has for it, without the CLIP embedding
+- its keywords in place of that embedding (see "Backup layout")
+- for an image, the EXIF and XMP of its original, and its dimensions if it is a
+  JPEG
+- for a live photo, the same for its image
+
+The backup runs unattended from cron (see "Running the backup from cron").
+
+`quak helper list-missing-thumbnails` finds files whose thumbnail is missing.
+`quak helper fix-missing-thumbnails` makes a new thumbnail for such a file, then
+encrypts it and uploads it to the server.
 
 ## Getting Started
 
@@ -60,10 +70,11 @@ const client = await Client.login({
     password: "your-password",
 });
 
-// Open a cache-backed library. On an empty cache this awaits one server
+// Open a cache-backed library. On an empty cache, or one that only
-// refresh; on an existing cache it returns immediately and refreshes in the
+// `lib.refreshCollection()` wrote, this awaits one server refresh. Otherwise
-// background. Later refreshes start `refreshIntervalSeconds` (default 3) after
+// it returns immediately and refreshes in the background. A background timer
-// the previous one ends.
+// then refreshes again `refreshIntervalSeconds` (default 3) after its previous
+// refresh ends.
 const lib = await Library.open({ client });
 
 // Default reads answer synchronously from the local cache — no network.
@@ -680,22 +691,40 @@ quak helper fix-missing-thumbnails [--file ids] [--json]  generate + upload miss
 ```
 
 Every command except `login`, `whoami` and `logout` runs on the cache-backed
-library. The read commands — `collections`, `files`, `get`, `get-thumb`,
+library. Each read command makes a fresh server round-trip before it answers. It
-`backup-metadata`, `helper list-missing-thumbnails` and
+then reports the account's current state, not what the cache last held. The read
-`helper fix-missing-thumbnails` — force a fresh server round-trip before they
+commands are:
-answer, so they report current account state rather than whatever the cache last
+
-held. `collections` asks the server for the collection list alone, in one
+- `collections`
-request, and neither fetches any collection's files nor changes the cache. The
+- `files`
-others wait for a refresh. With an empty cache, as on a first run, that refresh
+- `get`
-fetches the files of every collection, one collection after another, and stores
+- `get-thumb`
-nothing until it has them all, which on a large account takes a while. Meanwhile
+- `backup-metadata`
-the command logs a line on stderr for each collection whose files it has
+- `helper list-missing-thumbnails`
-fetched, such as `Fetched the files of 3 of 120 collections`, with `--json` too;
+- `helper fix-missing-thumbnails`
-`backup` does the same while the refresh it starts with runs. stdout holds only
+
-the command's output. If that round-trip fails, the command prints the error on
+`collections` asks the server for the collection list alone, in one request. It
-one line and exits 1, or 3 when the server no longer accepts the saved session
+fetches no collection's files and leaves the cache as it is. `files` with a
-(see "Session handling"). An album or file quak cannot decrypt does not fail it;
+collection ID asks for the collection list the same way. It then asks for the
-the command answers from what did decrypt (see "Default reads vs. fresh reads").
+files of that collection alone, and stores them in the cache. It asks for no
+files when the cache's copy of that collection is current. The other read
+commands, and `files` without a collection ID, wait for a refresh. So does
+`files` with the ID of a collection that is new since the last refresh.
+
+The first refresh fetches the files of every collection, one collection after
+another. That includes any collection that `files` with a collection ID stored
+before it. The refresh stores nothing until it has them all, and on a large
+account that takes a while. Meanwhile the command logs a line on stderr for each
+collection whose files it has fetched, such as
+`Fetched the files of 3 of 120 collections`. It logs these lines with `--json`
+too. `backup` logs them during the refresh it starts with. stdout holds only the
+command's output.
+
+If the server round-trip fails, the command prints the error on one line. It
+exits 1, or 3 when the server no longer accepts the saved session (see "Session
+handling"). An album or file that quak cannot decrypt does not fail the command.
+The command answers from what did decrypt (see "Default reads vs. fresh reads").
+
 `--cache-dir` overrides where the cache lives; without it each account gets its
 own directory under the per-user cache path.
 
@@ -750,9 +779,10 @@ its `Failed files:` list. Every other line is logged as it is without `--json`.
 exit status 1.
 
 `files <collectionID>` lists the files in that collection. `files` with no
-argument lists every file in the account, collection by collection, each file
+argument lists every file in the account once, collection by collection. The
-once: a file in several collections is listed with the first of them, which is
+collections come in the order the server first sent them in a refresh. A file in
-its `collectionID` in `--json`.
+several collections is listed with the first of them, which is its
+`collectionID` in `--json`.
 
 An ID given to `files`, `get`, `get-thumb` or
 `helper fix-missing-thumbnails --file` is written in decimal digits, no larger
@@ -1092,15 +1122,17 @@ against a fake of the Ente HTTP API, and `yarn test` verifies them.
 ### Opening a library
 
 `Library.open(options)` loads the on-disk cache, starts the background refresh
-loop, and resolves to a `Library`. On an empty cache it awaits the first
+loop, and resolves to a `Library`. On an empty cache, or one that only
-refresh, so it opens onto the account's data whenever the server is reachable;
+`lib.refreshCollection()` wrote, it awaits one refresh. It then opens onto the
-if that refresh fails, it opens with no data and records the error in
+account's data whenever the server is reachable. If that refresh fails, it opens
-`lib.status()`. On an existing cache it returns immediately and refreshes in the
+onto what the cache holds, and records the error in `lib.status()`. On any other
-background, so an unreachable server does not block opening. With
+cache it returns immediately and refreshes in the background. An unreachable
-`refreshOnOpen: false` it starts no refresh and returns at once onto what the
+server then does not block opening.
-cache holds, empty or not; a refresh then starts only when `fresh()` or
+
-`lib.backup()` asks, or the background timer fires. The CLI's read commands open
+With `refreshOnOpen: false`, `open()` starts no refresh. It returns at once onto
-it so (see "CLI surface").
+what the cache holds, even when the cache is empty. A refresh then starts only
+when `fresh()` or `lib.backup()` asks, or the background timer fires. The CLI's
+read commands open the library this way (see "CLI surface").
 
 `LibraryOptions`:
 
@@ -1127,22 +1159,35 @@ when the library opens; `lib.downloadDirectory` holds the result.
 `onProgress` receives a `RefreshEvent` with status `"started"` as a refresh, an
 ML data fetch or a precache sweep starts, and `"done"` or `"failed"` as it ends.
 In between, a refresh sends `"progress"` after each collection whose files it
-fetched, with `fetched`, how many collections it has fetched the files of so
+fetched. That event's `fetched` is the number of collections whose files the
-far, and `total`, how many it will. A refresh fetches the files of each
+refresh has fetched so far. Its `total` is the number of collections whose files
-collection that is new or changed since the cache's copy, so on an empty cache
+it will fetch in all. A refresh fetches the files of each collection that is new
-it fetches those of every collection.
+or changed since the cache's copy. On the first refresh, that is every
+collection.
 
 Concurrency is set through `pools`: construct
 `new RequestPools({ metadataConcurrency, contentConcurrency, thumbnailConcurrency })`
 and pass it. The three pools default to 10 / 5 / 25 (see Request pools below).
 
-`lib.status()` returns a `LibraryStatus` (collection/file counts, last
+`lib.status()` returns a `LibraryStatus`, which holds:
-refresh/ML times and errors, originals usage and effective limit, precache
+
-progress, and `closed`). `lib.close()` stops the background timer; it is
+- the collection and file counts
-idempotent, and an in-flight refresh is left to finish. The promise it returns
+- the time of the last refresh that succeeded, and the error of the latest
-resolves once that refresh (including its cache write), the ML data fetch and
+  refresh if it failed
-the precache fetches already running have all finished, so the cache directory
+- the same two for the ML data fetch
-can then be removed.
+- the originals cache's usage and its effective limit
+- the precache progress
+- `closed`
+
+`lib.close()` stops the background timer, and is idempotent. A refresh or
+`lib.refreshCollection()` in flight is left to finish. `close()` returns a
+promise that resolves once all of these have finished:
+
+- that refresh or `lib.refreshCollection()`, with its cache write
+- the ML data fetch
+- the precache fetches already running
+
+The cache directory can then be removed.
 
 `lib.status().mlDataErrors` lists, as `{ fileID, error }`, each file whose ML
 data the last ML data fetch that succeeded got but could not decrypt, gunzip or
@@ -1156,39 +1201,72 @@ cache.
 
 Default reads — `lib.albums`, `lib.photos`, `lib.timeline` — answer
 synchronously from the copy held in RAM and never touch the network. A refresh
-changes that copy only once all its server requests have succeeded, and the
+changes that copy only once all its server requests have succeeded.
-background timer starts the next refresh `refreshIntervalSeconds` after the
+`lib.refreshCollection()` changes it the same way for one collection. So a
-previous one ends. So a default read is immediate, but only as current as the
+default read is immediate, but only as current as the last refresh or
-last refresh whose requests all succeeded; right after opening an existing
+`lib.refreshCollection()` whose requests all succeeded. Right after `open()`
-cache, it is the copy on disk.
+returns without awaiting a refresh, that copy is the one loaded from disk.
 
-`await lib.fresh()` waits for a refresh to complete and persist, and returns the
+The background timer takes a turn `refreshIntervalSeconds` after its last turn
-same `{ albums, photos, timeline }` namespaces, which then reflect a completed
+ends. Each turn starts a refresh, unless a refresh or `lib.refreshCollection()`
-server round-trip. When a refresh is already running, background or not,
+is already running.
-`fresh()` waits for that one, so its answer can come from requests made before
+
-the call; only when none is running does it start one. A refresh that fails
+`await lib.fresh()` waits for a refresh to complete and persist. It then returns
+the same `{ albums, photos, timeline }` namespaces, which reflect a completed
+server round-trip. If a `lib.refreshCollection()` is running, `fresh()` first
+waits for it to end. When a refresh is already running, background or not,
+`fresh()` waits for that one. Its answer can then come from requests made before
+the call. Only when none is running does it start one. A refresh that fails
 rejects the caller (default reads stay silent and keep serving the last good
-copy). The CLI's read commands use fresh reads (issue
+copy). Every CLI read command calls `fresh()`, except `quak collections`.
-https://git.eeqj.de/sneak/quak/issues/75).
+`quak files` with a collection ID calls it only when `lib.refreshCollection()`
+resolves to `false`.
 
-`await lib.freshCollections()` is the fresh read of the collection list alone:
+`await lib.freshCollections()` is the fresh read of the collection list alone.
-one collections request, answered with every live collection that decrypts, as
+It sends one collections request. It answers with every live collection that
-the `Collection` objects `listCollections()` returns, in the server's order. It
+decrypts, in the server's order, as the `Collection` objects that
-fetches no collection's files and stores nothing, not even the list: a refresh
+`listCollections()` returns. It fetches no collection's files and stores
-fetches a collection's files only when the collection is new or has changed
+nothing, not even the list. A refresh fetches a collection's files only when the
-since the stored copy, so a collection stored without its files would never get
+collection is new or has changed since the stored copy. So a collection stored
-them. `quak collections` uses it (issue
+without its files would never get them. `quak collections` uses
-https://git.eeqj.de/sneak/quak/issues/210).
+`freshCollections()`.
 
-An album or file in the server's answer that quak cannot decrypt, or whose
+`await lib.refreshCollection(collection)` brings one collection up to date in
-metadata is not JSON, does not fail the refresh. The refresh leaves it out, an
+the cache, given its `Collection` from `freshCollections()`. It does for that
-album with all its files, and drops any older copy the cache held, so reads
+collection what a refresh does for a changed one, and fetches no other
-answer from what did decrypt. The library keeps a list of what it left out, with
+collection's files. It fetches the collection's files changed since the cache's
-the reason, in `metadata.json`: the next refresh asks the server only for what
+copy, or all of them when the cache has no copy. It then stores and saves them.
-changed, so it would not see the record again. A record stays on that list until
+It sends no request when the cache's copy has the same `updationTime` or a later
-a later refresh gets a copy that decrypts or learns that the server deleted it.
+one. It resolves to `true` when the cache then holds the collection.
-`lib.backup()` reports each such album, and each such file in its scope that has
+
-no copy that decrypted (see "Backup layout").
+`lib.refreshCollection()` adds a collection the cache does not hold only while
+the refresh cursor is 0. The cursor moves past 0 once a refresh receives the
+account's collections. After that, for a collection the cache does not hold, it
+sends no request and resolves to `false`. Such a collection is new since that
+refresh, or the refresh dropped it. Only a refresh may then add it, after the
+collections the cache holds.
+
+A refresh from a cursor of 0 replaces everything the cache holds. It fetches the
+files of every collection, even those `lib.refreshCollection()` stored. It
+stores the collections in the server's order. The cache then holds what it would
+had `lib.refreshCollection()` never run.
+
+`lib.refreshCollection()` leaves the refresh cursor where it was, so the next
+refresh still fetches the files of every other collection that changed. It never
+runs at the same time as a refresh. It first waits for a running refresh or
+`lib.refreshCollection()` to end. While it runs, a `fresh()` or `lib.backup()`
+waits for it to end. `quak files` with a collection ID uses it.
+
+A refresh does not fail on an album or file that quak cannot decrypt, or whose
+metadata is not JSON. The refresh leaves out such a file, and such an album
+together with all its files. It also drops any older copy that the cache held,
+so reads answer from what did decrypt. The library keeps a list of what it left
+out, with the reason, in `metadata.json`. The next refresh asks the server only
+for what changed, so it would not see them again. An entry stays on that list
+until a later refresh or `lib.refreshCollection()` stores a copy that decrypts,
+or learns that the server deleted it. `lib.backup()` reports each such album,
+and each such file in its scope that has no copy that decrypted (see "Backup
+layout").
 
 ### Read surface
 
@@ -1282,10 +1360,17 @@ The GUI-facing records hold no key material and no binary, so they survive
 - `LibrarySnapshot`: `{ albums, photos, takenAt }`.
 
 `lib.snapshot()` returns a `LibrarySnapshot` (albums newest-updated first,
-photos newest first). `lib.subscribe({ onChange })` delivers a `LibraryChange`
+photos newest first). `lib.subscribe({ onChange })` returns `{ unsubscribe }`.
-(`albumsChanged`, `photosChanged`, `fileIDsRemoved`, `albumIDsRemoved`,
+It calls `onChange` with a `LibraryChange` whenever a refresh or
-`refreshedAt`) whenever a refresh alters the projection, and returns
+`lib.refreshCollection()` changes these records. A refresh or
-`{ unsubscribe }`; a refresh that changes nothing delivers nothing.
+`lib.refreshCollection()` that changes nothing does not call it. A
+`LibraryChange` holds:
+
+- `albumsChanged`
+- `photosChanged`
+- `fileIDsRemoved`
+- `albumIDsRemoved`
+- `refreshedAt`
 
 ### Thumbnails, ML search, and backup
 
@@ -1301,29 +1386,44 @@ photos newest first). `lib.subscribe({ onChange })` delivers a `LibraryChange`
   `SimilarResult[]` (`{ fileID, score }`, cosine similarity, most similar first,
   default limit 20). quak bundles no text encoder, so `searchByEmbedding` takes
   a query vector the caller produced elsewhere.
-- `await lib.backup(opts?)` → `BackupResult`. It takes the lock in the download
+- `await lib.backup(opts?)` → `BackupResult`. It takes the lock, `backup.lock`
-  directory, and fails at once with an error whose `code` is `ELOCKED` while
+  in the download directory. It fails at once with an error whose `code` is
-  another backup of it runs. A caller can instead take the lock itself, before
+  `ELOCKED` while another backup of that directory runs. A caller can instead
-  it opens its library, as `quak backup` does: `await lockBackupDirectory(dir)`
+  take the lock itself before it opens its library, as `quak backup` does.
-  takes it, failing the same way, and returns a `BackupLock`, whose `release()`
+  `await lockBackupDirectory(dir)` takes it, failing the same way, and returns a
-  removes the lock unless it was lost and whose `lost` holds why it was lost.
+  `BackupLock`. Its `release()` removes the lock unless it was lost, and its
-  The caller passes it to the backup as `lock`, and releases it once the backup
+  `lost` holds why it was lost. The caller passes it to the backup as `lock`,
-  ends. It waits for a refresh as `fresh()` does, puts every in-scope original
+  and releases it once the backup ends.
-  not already at its save path there as `photo.download()` does (and, with
+
-  `includeThumbnails`, fetches thumbnails) through the content cache, waits for
+    The backup waits for a refresh as `fresh()` does. It then fetches each
-  an ML data fetch, and rebuilds the on-disk backup tree with a durable failure
+    in-scope original that is not yet at its save path, as `photo.download()`
-  ledger. Each file's JSON holds its ML data and keywords. An image's JSON also
+    does, through the content cache. With `includeThumbnails` it also fetches
-  holds the EXIF and XMP of its original, and its dimensions if it is a JPEG. A
+    thumbnails. It waits for an ML data fetch, then rebuilds the backup tree. It
-  live photo's JSON holds these for its image. A video's JSON holds no EXIF, XMP
+    records each file that failed in `failures.json`.
-  or dimensions. A fetched original is written straight to its save path and not
+
-  into the cache, which then counts it as present; one the cache already held is
+    Each file's JSON holds its ML data and keywords. An image's JSON also holds
-  copied from there. `BackupOptions`: `downloadDirectory` (falls back to the
+    the EXIF and XMP of its original, and its dimensions if it is a JPEG. A live
-  library's), `includeOriginals` (default `true`), `includeThumbnails` (default
+    photo's JSON holds these for its image. A video's JSON holds no EXIF, XMP or
-  `false`), `onlyAlbumNames`, `verify` (default `false`), `onProgress`, and
+    dimensions.
-  `lock`. See Backup layout above for the tree it writes, and for the albums
+
-  `BackupResult` lists in `undecryptableAlbums` and `failedAlbums`. Whether the
+    A fetched original is written straight to its save path, not into the cache.
-  backup took the lock or its caller did, once the lock is lost the backup
+    The cache then counts it as present. An original that the cache already held
-  rejects with `lost the lock on <dir>: <reason>` before it starts another file.
+    is copied from there.
+
+    `BackupOptions` holds:
+    - `downloadDirectory`, which falls back to the library's
+    - `includeOriginals`, `true` by default
+    - `includeThumbnails`, `false` by default
+    - `onlyAlbumNames`
+    - `verify`, `false` by default
+    - `onProgress`
+    - `lock`
+
+    "Backup layout" above describes the tree that the backup writes. It also
+    describes the albums that `BackupResult` lists in `undecryptableAlbums` and
+    `failedAlbums`. Once the lock is lost, the backup rejects with
+    `lost the lock on <dir>: <reason>` before it starts another file. This holds
+    whether the backup or its caller took the lock.
 
 ### Request pools
 

TODO.md

@@ -26,6 +26,21 @@ declares one.
 
 # Completed Steps
 
+- 2026-10-25: `quak files COLLECTION` fetches the files of that collection alone
+  (https://git.eeqj.de/sneak/quak/issues/217). It used to wait for a refresh,
+  which on an empty cache fetched the files of every collection first. It now
+  reads the collection list through `lib.freshCollections()`, then brings that
+  one collection up to date through the new `lib.refreshCollection()`. That
+  stores and saves its files as a refresh would, and leaves the refresh cursor
+  where it was. When the stored copy is current, it asks for none of the files.
+  It never runs at the same time as a refresh. Once a refresh has received the
+  account's collections, it stores no collection the cache does not hold, and
+  `quak files COLLECTION` waits for a refresh instead. A refresh from a cursor
+  of 0 replaces all the cache holds, so collections keep the server's order. A
+  library opened on a cache that only `lib.refreshCollection()` wrote awaits its
+  first refresh. `quak files` with no argument still waits for a refresh. The
+  store lists what did not decrypt by collection ID and file ID.
+
 - 2026-10-22: The JSON `quak backup` and `quak backup-metadata` write for a file
   holds `keywords` in place of the CLIP embedding in its ML data
   (https://git.eeqj.de/sneak/quak/issues/218). The keywords are the titles of

src/cli-commands.ts

@@ -128,12 +128,13 @@ const readLibraryClient = (client: Client): LibraryClient => ({
     contentSource: () => client.contentSource(),
 });
 
-// Open a library for a single point command: the aggressive background precache
+// Open a library for a single point command. The aggressive background
-// (issue #48) is off — a one-shot `collections` or `get` must not start
+// precache (issue #48) is off, because a one-shot `collections` or `get` must
-// downloading the whole account — and no refresh starts as it opens or on a
+// not start downloading the whole account. No refresh starts as it opens or on
-// timer: each command asks for the one it needs, and `collections` needs none
+// a timer. Each command asks for the refresh it needs, and `collections` and
-// (issue #210). While a refresh runs, each collection whose files it has
+// `files COLLECTION` need none (issues #210 and #217). While a refresh runs,
-// fetched is logged, so a large account shows progress rather than nothing.
+// each collection whose files it has fetched is logged, so a large account
+// shows progress rather than nothing.
 const openReadLibrary = (ctx: CliContext, client: Client): Promise<Library> =>
     Library.open({
         client: readLibraryClient(client),

src/cli-read.ts

@@ -2,33 +2,42 @@
 //
 // `collections`, `files`, `get`, and `get-thumb` must answer for
 // the account's state at the moment the command runs, not for whatever the
-// local cache last happened to hold (owner amendment, issue #36). `files`,
+// local cache last happened to hold (owner amendment, issue #36). `files`
-// `get` and `get-thumb` therefore force a server round-trip through
+// without a collection ID, `get` and `get-thumb` therefore force a server
-// `Library.fresh()` and only then read — so a collection, file, or metadata
+// round-trip through `Library.fresh()`, and only then read. A collection, file,
-// change made elsewhere is visible. `collections` asks the library for the
+// or metadata change made elsewhere is then visible. `collections` asks the
-// collection list alone through `Library.freshCollections()` (issue #210): a
+// library for the collection list alone through `Library.freshCollections()`
-// refresh would also fetch the files of every collection, which on a large
+// (issue #210). A refresh would also fetch the files of every collection, which
-// account takes long and which `collections` does not print.
+// `collections` does not print, and on a large account that takes long.
+// `files COLLECTION` reads the collection list the same way, for the same
+// reason. It then brings that one collection up to date through
+// `Library.refreshCollection()` (issue #217), and fetches no other collection's
+// files. Once a refresh has received the account's collections,
+// `refreshCollection()` stores no collection the library does not hold.
+// `files COLLECTION` then forces a refresh instead.
 //
-// `collections` lists in the server's order and `files` in the library's own
+// `collections` lists in the server's order. `files` lists in the library's
-// enumeration order (`listFiles()`), the orders the pre-library CLI printed,
+// own enumeration order: `listCollections()`, then `listFiles()` for each.
-// rather than the `albums`/`photos` projection's newest-first order, which
+// Those are the orders the pre-library CLI printed. The `albums`/`photos`
-// re-sorts the rows. The field values still come from each record's raw
+// projection would re-sort the rows newest first. After a refresh, the
-// metadata via `cli-output.ts`. `files` without a collection ID lists every
+// library holds collections in the order the server first sent them. The
-// file in the account once (issue #211): the library keeps a record of a file
+// field values still come from each record's raw metadata via
-// for each collection that holds it, and only the first collection's record is
+// `cli-output.ts`. `files` without a collection ID lists every file in the
-// listed.
+// account once (issue #211).
+// The library keeps a record of a file for each collection that holds it, and
+// only the first collection's record is listed.
 
 import type { Collection, EnteFile } from "./model/types.js";
 import type { Photo, PhotosAPI } from "./library/index.js";
 
 // The slice of `Library` these helpers read. `Library` satisfies it
-// structurally; a test can drive them with a stand-in that records the
+// structurally. A test can drive them with a stand-in that records the
-// `fresh()` and `freshCollections()` calls and serves records in a known
+// `fresh()`, `freshCollections()` and `refreshCollection()` calls. The
-// enumeration order.
+// stand-in serves records in a known enumeration order.
 export interface FreshReadLibrary {
     fresh(): Promise<unknown>;
     freshCollections(): Promise<Collection[]>;
+    refreshCollection(collection: Collection): Promise<boolean>;
     getCollection(id: number): Collection | undefined;
     listCollections(): Collection[];
     listFiles(collectionID: number): EnteFile[];
@@ -42,21 +51,29 @@ export const freshCollections = (
     lib: FreshReadLibrary,
 ): Promise<Collection[]> => lib.freshCollections();
 
-// The files of one collection, current as of a forced refresh, in enumeration
+// The files of one collection, in enumeration order. `undefined` (not an empty
-// order. `undefined` (not an empty list) when the collection does not exist, so
+// list) when the collection does not exist, so the caller can tell "no such
-// the caller can tell "no such collection" from "an empty collection". Without
+// collection" from "an empty collection". They are current as of one
-// a collection ID, every file in the account, each once, as held by the first
+// collections request and the requests that bring that collection alone up to
-// collection that holds it.
+// date. When `refreshCollection()` stores nothing, they are current as of a
+// forced refresh instead. Without a collection ID, every file in the account,
+// current as of a forced refresh. Each file is listed once, as held by the
+// first collection that holds it.
 export const freshFiles = async (
     lib: FreshReadLibrary,
     collectionID?: number,
 ): Promise<EnteFile[] | undefined> => {
-    await lib.fresh();
     if (collectionID !== undefined) {
-        return lib.getCollection(collectionID)
+        const collections = await lib.freshCollections();
-            ? lib.listFiles(collectionID)
+        const collection = collections.find((c) => c.id === collectionID);
-            : undefined;
+        if (!collection) return undefined;
+        if (!(await lib.refreshCollection(collection))) {
+            await lib.fresh();
+            if (!lib.getCollection(collectionID)) return undefined;
+        }
+        return lib.listFiles(collectionID);
     }
+    await lib.fresh();
     const listed = new Set<number>();
     const files: EnteFile[] = [];
     for (const collection of lib.listCollections()) {

src/library/index.ts

@@ -1,28 +1,36 @@
 // The library surface over the local cache.
 //
 // `Library.open()` loads the on-disk metadata store (issue #41), then starts
-// the refresh loop. When the cache loaded empty it awaits the first refresh,
+// the refresh loop. When the stored cursor is 0, `open()` awaits the first
-// so the library never opens onto an empty store it could have filled; when an
+// refresh. No refresh has then stored any collection: the cache is empty, or
-// existing copy loaded, that first refresh runs in the background and `open()`
+// holds only what `refreshCollection()` stored. The library must not serve
-// returns as soon as the cached data is ready to serve — a slow or unreachable
+// that as the whole account. Otherwise that first refresh runs in the
-// server no longer stalls opening. A background timer then refreshes every
+// background. `open()` returns as soon as the cached data is ready to serve,
-// `refreshIntervalSeconds`. Every default read is answered from RAM — no
+// so a slow or unreachable server does not stall opening. A background timer
-// default read touches the network. There is deliberately no `sync()`, no
+// then takes a turn `refreshIntervalSeconds` after its last turn ends. Each
-// `refresh()`, no `serverReachable` flag, and no "before each read" mode
+// turn starts a refresh, unless a refresh or `refreshCollection()` is already
-// (design #36).
+// running. Every default read is answered from RAM — no default read touches
+// the network. There is deliberately no `sync()`, no `refresh()`, no
+// `serverReachable` flag, and no "before each read" mode (design #36).
 //
-// `fresh()` is the one exception (issue #75, an owner amendment to #36): it
+// `fresh()` is an exception (issue #75, an owner amendment to #36). It awaits
-// forces a refresh, awaits it, and only then hands back the read namespaces, so
+// a refresh, and only then hands back the read namespaces. A caller that needs
-// a caller that needs server-current data can ask for it. Concurrent `fresh()`
+// server-current data uses it. Concurrent `fresh()` calls coalesce onto one
-// calls coalesce onto one in-flight refresh, and a refresh that fails rejects
+// in-flight refresh. A refresh that fails rejects the caller. The default
-// the caller (the default reads stay silent and serve the last good copy). The
+// reads stay silent and serve the last good copy. The default methods and the
-// default methods and the background loop are unchanged.
+// background loop are unchanged.
 //
 // `freshCollections()` is the fresh read of the collection list alone (issue
-// #210): one collections request, no collection's files, and nothing stored,
+// #210). It sends one collections request and stores nothing.
-// for a caller such as `quak collections` that needs no more. A caller that
+// `quak collections` uses it. `refreshCollection()` brings one collection
-// asks for each refresh it needs can also open the library with
+// from that list up to date in the store (issue #217). It fetches that
-// `refreshOnOpen: false`, so that `open()` starts none.
+// collection's files alone, as a refresh would. `quak files COLLECTION` uses
+// it. It never runs at the same time as a refresh. Once the stored cursor is
+// past 0, it only updates a collection the store holds, and only a refresh
+// adds one. A refresh from a stored cursor of 0 replaces all the store holds.
+// So the store keeps collections in the server's order. A caller that asks for
+// each refresh it needs can also open the library with `refreshOnOpen: false`,
+// so that `open()` starts none.
 //
 // A refresh reports through `onProgress` each collection whose files it has
 // fetched, so a large account, whose first refresh fetches the files of every
@@ -31,10 +39,12 @@
 // A refresh stages all of its network work first and only mutates the store
 // once every fetch has succeeded. A refresh that fails partway therefore never
 // becomes visible to reads: the last good snapshot stays in place, and the
-// failure surfaces through `onProgress` and `status()` instead. A commit that
+// failure surfaces through `onProgress` and `status()` instead. A save can
-// mutates RAM but then fails to persist keeps `status().lastError` set and the
+// still fail after the store has changed in RAM. The store then stays marked
-// store marked unsaved until a later save actually lands, so a stuck disk is
+// unsaved until a later save lands. Until then, every `commit()` retries the
-// never masked by a subsequent empty refresh.
+// save. A refresh whose save fails sets `status().lastError`, which stays set
+// until a later refresh succeeds. `refreshCollection()` never sets or clears
+// it. So a stuck disk is never hidden by a later refresh that changes nothing.
 
 import { rm } from "node:fs/promises";
 import { join, resolve } from "node:path";
@@ -159,21 +169,23 @@ export interface LibraryClient {
         payloads: Map<number, MLData>;
         errors: Map<number, unknown>;
     }>;
-    // The byte source for the on-disk content cache. Optional so a mock client
+    // The byte source for the on-disk content cache. Optional, so a mock
-    // that only serves metadata still satisfies the interface; when absent (and
+    // client that only serves metadata still satisfies the interface. Without
-    // no explicit `contentSource` is passed to `open`) the content cache is
+    // it, and with no `contentSource` passed to `open`, the content cache is
-    // disabled and `Photo.original`/`thumbnail` and `thumbnails.ensure` throw.
+    // disabled. `Photo.original`/`thumbnail` and `thumbnails.ensure` then
+    // throw.
     contentSource?(): ContentSource;
 }
 
-// A progress event for one unit of background work. A metadata "refresh" or an
+// A progress event for one unit of background work. A metadata "refresh" and
-// ML "fetchMLData" pass each fire "started" before their network work and then
+// an ML "fetchMLData" pass each fire "started" before their network work. Each
-// exactly one of "done" or "failed"; "failed" carries the error message and
+// then fires exactly one of "done" or "failed". A "failed" event carries the
-// an ML "done" reports how many payloads it stored and, in `mlDataErrors`,
+// error message. An ML "done" reports in `fetched` how many payloads it
-// each file whose ML data did not decrypt, gunzip or parse, with the reason.
+// stored. Its `mlDataErrors` lists each file whose ML data did not decrypt,
-// In between, a refresh fires "progress" after each collection whose files it
+// gunzip or parse, with the reason. In between, a refresh fires "progress"
-// fetched: `fetched` is how many collections it has fetched the files of so
+// after each collection whose files it fetched. Its `fetched` is how many
-// far, `total` how many it will. The precache fills
+// collections it has fetched the files of so far, and `total` how many it
+// will. The precache fills
 // ("precacheThumbnails"/"precacheOriginals", #48) fire "started"/"done" around
 // each sweep that has work, "done" reporting the count newly cached.
 export interface RefreshEvent {
@@ -201,9 +213,10 @@ export interface LibraryOptions {
     // directory at open. The content cache treats an original already stored
     // at its save path as present.
     downloadDirectory?: string;
-    // How long after one refresh ends the background timer starts the next.
+    // How long after its last turn ends the background timer takes the next.
-    // `Infinity` starts none: the library then refreshes only as it opens and
+    // A turn starts a refresh unless a refresh or `refreshCollection()` is
-    // when `fresh()` or `backup()` asks.
+    // running. With `Infinity` the timer takes no turn: the library then
+    // refreshes only as it opens and when `fresh()` or `backup()` asks.
     refreshIntervalSeconds?: number;
     // Whether `open()` starts a refresh. Defaults to true. With false, `open()`
     // returns at once onto what the cache holds, empty or not, and a refresh
@@ -242,8 +255,9 @@ export interface LibraryStatus {
     // Wall-clock ms of the last refresh that succeeded, or undefined if none
     // has yet.
     lastRefreshAt?: number;
-    // The message from the most recent refresh, set only while that refresh
+    // The error of the most recent refresh, set only when it failed. The next
-    // failed; cleared by the next success.
+    // refresh that succeeds clears it. `refreshCollection()` never sets or
+    // clears it.
     lastError?: string;
     // Wall-clock ms of the last ML fetch pass that succeeded, or undefined if
     // none has yet (or ML fetching is disabled).
@@ -306,12 +320,17 @@ export class Library {
     private readonly precache?: Precache;
 
     private timer?: ReturnType<typeof setTimeout>;
-    // The in-flight refresh cycle, or undefined when none runs. One slot serves
+    // The in-flight refresh cycle or `refreshCollection()`, or undefined when
-    // both paths: the background loop skips when it is set, and a fresh read
+    // neither runs. One slot holds both, so they never run at the same time.
-    // (issue #75) coalesces onto it or starts one. The promise carries the
+    // The background loop skips while it is set. A fresh read (issue #75)
-    // cycle's real outcome (it rejects on failure); the background loop ignores
+    // coalesces onto a running refresh. It waits for a running
-    // that, a fresh read propagates it.
+    // `refreshCollection()` to end, and then joins or starts a refresh. The
+    // promise carries the real outcome: it rejects on failure. The background
+    // loop ignores a failure. A fresh read passes on the failure of the
+    // refresh it joins or starts, and `refreshCollection()` passes on its own.
     private cycle?: Promise<void>;
+    // Whether `cycle` is a refresh cycle rather than a `refreshCollection()`.
+    private cycleIsRefresh = false;
     // Guards the ML fetch pass so a slow backfill never runs twice at once; a
     // refresh whose pass is still running kicks nothing new. Holds the running
     // pass, so `close()` and `backup()` can wait for it. It rejects when the
@@ -324,19 +343,20 @@ export class Library {
     private lastMLError?: string;
     // For each file whose ML data the last ML fetch pass that succeeded got
     // but could not decrypt, gunzip or parse, why not, by fileID. A pass
-    // gathers its own and puts them here when it ends without failing, so
+    // gathers its own and puts them here only when it ends without failing.
-    // `status()` and `backup()` never see the list of a pass that is still
+    // So `status()` and `backup()` never see the list of a pass still running
-    // running or that failed. Kept in RAM only, never in the cache.
+    // or one that failed. Kept in RAM only, never in the cache.
     private mlDataErrors = new Map<number, unknown>();
-    // The plain-record projection as of the last refresh, and the GUI change
+    // The plain-record projection as of the last store change, and the GUI
-    // subscribers. A refresh that alters the projection notifies each with the
+    // change subscribers. A refresh or `refreshCollection()` that alters the
-    // delta; `lastRecords` is kept current every refresh so a subscriber that
+    // projection notifies each subscriber with the delta. `lastRecords`
-    // joins later diffs against the state its own `snapshot()` already returned.
+    // advances on each `commit()` that changes the store. A subscriber that
+    // joins later then diffs against the state its own `snapshot()` returned.
     private readonly subscribers = new Set<(change: LibraryChange) => void>();
     private lastRecords: DerivedRecords;
     // RAM holds changes disk has not yet accepted (an earlier save failed).
-    // Cleared only when a save actually succeeds; keeps the store trying to
+    // Cleared only when a save succeeds. Until then, every `commit()` retries
-    // persist and the failure visible in `status()` until then.
+    // the save.
     private unsaved = false;
 
     private constructor(args: {
@@ -366,7 +386,7 @@ export class Library {
         this.lastRecords = this.deriveNow();
 
         // The read namespaces derive fresh from the store on each call, so they
-        // always reflect the latest refresh.
+        // always reflect what it holds now.
         const derive = (): DerivedRecords => this.deriveNow();
         const root = this.downloadDirectory;
         const saves: SavePathLookup = {
@@ -393,14 +413,16 @@ export class Library {
         this.mldata = makeMLDataAPI(() => this.mlStore);
     }
 
-    // Load the cache and start the refresh loop. With an empty cache the first
+    // Load the cache and start the refresh loop. When the stored cursor is 0,
-    // refresh is awaited, so `open()` resolves onto populated data whenever the
+    // the first refresh is awaited. Such a cache is empty, or holds only what
-    // server is reachable; that awaited refresh may still fail, and the library
+    // `refreshCollection()` stored. `open()` then resolves onto the whole
-    // then opens empty with the failure recorded in `status()`. With an
+    // account whenever the server is reachable. If that refresh fails, the
-    // existing cache the first refresh runs in the background and `open()`
+    // library opens onto what the cache holds, with the failure recorded in
-    // returns as soon as the cached data is ready — an unreachable server does
+    // `status()`. With any other cache the first refresh runs in the
-    // not block opening. With `refreshOnOpen: false` there is no first
+    // background, and `open()` returns as soon as the cached data is ready.
-    // refresh: `open()` returns onto the cache as it is.
+    // An unreachable server then does not block opening. With
+    // `refreshOnOpen: false` there is no first refresh: `open()` returns onto
+    // the cache as it is.
     static async open(opts: LibraryOptions): Promise<Library> {
         const { userID } = opts.client.whoami();
         const cacheDirectory =
@@ -416,8 +438,8 @@ export class Library {
         let store = await MetadataStore.load(metadataPath);
         // A cache directory given explicitly can hold another account's cache.
         // Its records and cursor are not this account's, so delete it and the
-        // ML data beside it and start empty. A user ID of 0 means the cache
+        // ML data beside it and start empty. A user ID of 0 means nothing was
-        // was never refreshed and so holds nothing to discard.
+        // ever stored there, so there is nothing to discard.
         if (store.userID !== 0 && store.userID !== userID) {
             await rm(metadataPath, { force: true });
             await rm(join(cacheDirectory, "mldata"), {
@@ -440,10 +462,11 @@ export class Library {
             ? await MLDataStore.open(join(cacheDirectory, "mldata"))
             : undefined;
 
-        // Build the content cache from an explicit source or the client's own,
+        // Build the content cache from an explicit source or the client's own.
-        // and take its record of what is already cached (and reap orphan temp
+        // Take its record of what is already cached, and reap orphan temp
-        // files) before the first projection, so cached paths are present from
+        // files, before the first projection. Cached paths are then present
-        // the start and the first refresh raises no spurious path-change diff.
+        // from the start, and the first `commit()` raises no spurious
+        // path-change diff.
         const source = opts.contentSource ?? opts.client.contentSource?.();
         let cache: ContentCache | undefined;
         let precache: Precache | undefined;
@@ -497,22 +520,26 @@ export class Library {
             precache,
         });
 
-        // Start filling from whatever the loaded store already holds; each
+        // Start filling from whatever the loaded store already holds. Each
-        // refresh below re-kicks with the new files (and retries any that
+        // later `commit()` re-kicks the fills with its new files, and retries
-        // failed). An empty store starts empty here and fills after its first
+        // any that failed. An empty store starts empty here, and fills once a
-        // refresh.
+        // `commit()` stores files.
         precache?.start();
 
         if (opts.refreshOnOpen === false) {
             // The caller asks for each refresh it needs.
             lib.scheduleNext();
-        } else if (store.loadedFromDisk) {
+        } else if (store.collectionsSinceTime > 0) {
-            // An existing copy already answers reads; refresh in the background
+            // The stored cursor has moved, so a refresh has stored the
-            // and start the interval once that first cycle settles.
+            // account's collections and the cache's copy answers reads.
+            // Refresh in the background, and start the interval once that
+            // first cycle settles.
             void lib.runRefresh().then(() => lib.scheduleNext());
         } else {
-            // Nothing was cached: wait for the first refresh to fill the store
+            // The stored cursor is still 0, so no refresh has stored any
-            // (or fail) rather than resolve onto an empty library.
+            // collection: the cache is empty, or holds only what
+            // `refreshCollection()` stored. Wait for the first refresh to fill
+            // the store (or fail) rather than resolve onto part of the account.
             await lib.runRefresh();
             lib.scheduleNext();
         }
@@ -550,9 +577,9 @@ export class Library {
         return snapshotFrom(this.deriveNow(), Date.now());
     }
 
-    // Deliver a `LibraryChange` whenever a refresh alters the projection. A
+    // Deliver a `LibraryChange` whenever a refresh or `refreshCollection()`
-    // refresh that changes nothing delivers nothing. The returned handle's
+    // alters the projection. One that changes nothing delivers nothing. The
-    // `unsubscribe` stops delivery.
+    // returned handle's `unsubscribe` stops delivery.
     subscribe(args: { onChange: (change: LibraryChange) => void }): {
         unsubscribe: () => void;
     } {
@@ -595,12 +622,13 @@ export class Library {
         };
     }
 
-    // Fresh reads (issue #75, owner amendment to design #36). Force a refresh,
+    // Fresh reads (issue #75, owner amendment to design #36). Wait for a
-    // wait for it to complete and persist, then hand back the same
+    // refresh to complete and persist, then hand back the same
-    // `albums`/`photos`/`timeline` namespaces — now guaranteed to reflect a
+    // `albums`/`photos`/`timeline` namespaces. They then reflect a completed
-    // completed server round-trip. Concurrent calls coalesce onto one refresh;
+    // server round-trip. A running `refreshCollection()` is waited for first.
-    // a refresh that fails rejects here, where the default namespaces would
+    // Concurrent calls coalesce onto one refresh. A refresh that fails rejects
-    // instead stay silent and serve the last good copy.
+    // here, where the default namespaces would stay silent and serve the last
+    // good copy.
     async fresh(): Promise<FreshReads> {
         await this.refreshNow();
         return {
@@ -613,10 +641,10 @@ export class Library {
     // The fresh read of the collection list alone (issue #210): every live
     // collection that decrypts, in the server's order, from one collections
     // request. Unlike a refresh, it fetches no collection's files, which on a
-    // large account take long. Nothing is stored: a refresh fetches a
+    // large account take long. It stores nothing. A refresh fetches a
     // collection's files only when the collection is new or has changed since
-    // the stored copy, so a collection stored here without its files would
+    // the stored copy. A collection stored here without its files would never
-    // never have them fetched.
+    // have them fetched.
     async freshCollections(): Promise<Collection[]> {
         if (this.closed) throw new Error("the library is closed");
         const { collections } = await this.client.collectionsSince({
@@ -625,19 +653,44 @@ export class Library {
         return collections;
     }
 
+    // Bring one collection up to date in the store (issue #217), given its
+    // record from `freshCollections()`. It does for that collection what a
+    // refresh does for a changed one. It fetches no other collection's files.
+    // It resolves to whether the store then holds the collection.
+    //
+    // It adds a collection the store does not hold only while the stored
+    // cursor is 0, before any refresh has received a collection. After that,
+    // it stores nothing for such a collection and resolves to false. Only a
+    // refresh may then add it, after the collections the store holds.
+    //
+    // It runs in the same slot as a refresh, so the two never run at the same
+    // time. It first waits for a running refresh or `refreshCollection()` to
+    // end. While its own work runs, a fresh read or `backup()` waits for it,
+    // and the background loop skips its turn.
+    async refreshCollection(collection: Collection): Promise<boolean> {
+        while (this.cycle) await this.cycle.catch(() => {});
+        if (this.closed) throw new Error("the library is closed");
+        let held = false;
+        await this.startCycle(false, async () => {
+            held = await this.refreshCollectionOnce(collection);
+        });
+        return held;
+    }
+
     // Back up every in-scope file to `opts.downloadDirectory`, or else the
     // library's, each original at its save path, with a durable failure
-    // ledger (issue #51). Takes the lock in that directory first, unless the
+    // ledger (issue #51). It first takes the lock in that directory, unless
-    // caller passes the lock it took as `opts.lock`, failing at once while
+    // the caller passes the lock it took as `opts.lock`. Taking it fails at
-    // another backup of it runs, and before it starts another file once the
+    // once while another backup of that directory runs. Once the lock is lost,
-    // lock is lost (see `lockBackupDirectory`). Waits for a
+    // the backup fails before it starts another file (see
-    // completed refresh, as `fresh()` does, joining one already running, and
+    // `lockBackupDirectory`). It waits for a completed refresh as `fresh()`
-    // rejects before touching any file but the lock when it fails. Then puts
+    // does, joining one already running. When that refresh fails, it rejects
-    // pending originals at their save paths as `Photo.download()` does (and
+    // before touching any file but the lock. It then puts pending originals
-    // optional thumbnails) through the content cache and pools, waits for an
+    // at their save paths as `Photo.download()` does, through the content
-    // ML data fetch, and rebuilds the derived symlink/JSON views from the
+    // cache and pools. With `includeThumbnails` it also fetches thumbnails. It
-    // model, each file's JSON with its ML data, beside an `account.json` with
+    // waits for an ML data fetch. It rebuilds the derived symlink/JSON views
-    // the account's email and user ID.
+    // from the model, each file's JSON with its ML data. An `account.json`
+    // beside them holds the account's email and user ID.
     // Throws before any network work when no content cache backs the
     // originals it must fetch.
     backup(opts?: BackupOptions): Promise<BackupResult> {
@@ -674,12 +727,15 @@ export class Library {
         );
     }
 
-    // Stop the background timer. Idempotent. An in-flight refresh is left to
+    // Stop the background timer. Idempotent. A refresh or `refreshCollection()`
-    // finish; it will not schedule another cycle once closed. The returned
+    // in flight is left to finish, and nothing starts after it. The returned
-    // promise resolves once that refresh (including its cache write), the ML
+    // promise resolves once all of these have finished:
-    // fetch pass and the precache fetches already running have all finished,
+    //  - that refresh or `refreshCollection()`, with its cache write;
-    // so a caller can then remove the cache directory. A refresh failure is
+    //  - the ML fetch pass;
-    // reported through `status()`, not thrown here.
+    //  - the precache fetches already running.
+    // A caller can then remove the cache directory. A refresh failure is
+    // reported through `status()`, and a `refreshCollection()` failure to its
+    // own caller. Neither is thrown here.
     async close(): Promise<void> {
         this.closed = true;
         const precacheClosed = this.precache?.close();
@@ -702,33 +758,41 @@ export class Library {
         this.timer.unref?.();
     }
 
-    // The background loop's refresh: run a cycle unless one is already in flight
+    // The background loop's refresh: run a cycle unless a refresh or
-    // (or the library is closed), and never let a failure escape — the
+    // `refreshCollection()` is in flight (or the library is closed), and never
-    // background path reports errors through `status()`/`onProgress`, it does
+    // let a failure escape. The background path reports errors through
-    // not throw. Resolves once the cycle it started (or skipped past) settles.
+    // `status()`/`onProgress`; it does not throw. It resolves once the cycle
+    // it started settles, or at once when it starts none.
     private runRefresh(): Promise<void> {
         if (this.closed || this.cycle) return Promise.resolve();
-        return this.startCycle().catch(() => {});
+        return this.startCycle(true, () => this.refreshCycle()).catch(() => {});
     }
 
-    // A fresh read's refresh (issue #75): force a cycle and await it, rejecting
+    // A fresh read's refresh (issue #75): join the running refresh or start
-    // if it fails. Concurrent fresh reads coalesce onto the one in-flight cycle
+    // one, and await it, rejecting if it fails. Concurrent fresh reads
-    // — the background loop's included — so they never fan out into redundant
+    // coalesce onto the one in-flight cycle — the background loop's included —
-    // server round-trips.
+    // so they never fan out into redundant server round-trips. A running
-    private refreshNow(): Promise<void> {
+    // `refreshCollection()` is waited for first.
-        if (this.closed) {
+    private async refreshNow(): Promise<void> {
-            return Promise.reject(new Error("the library is closed"));
+        while (this.cycle && !this.cycleIsRefresh) {
+            await this.cycle.catch(() => {});
         }
-        return this.cycle ?? this.startCycle();
+        if (this.closed) throw new Error("the library is closed");
+        return this.cycle ?? this.startCycle(true, () => this.refreshCycle());
     }
 
-    // Start one refresh cycle and record it as the in-flight cycle so every
+    // Start `work` and record it in the in-flight slot, so every other caller
-    // caller coalesces onto it. The returned promise carries the cycle's real
+    // sees it. `isRefresh` says whether it is a refresh cycle, which a fresh
-    // outcome; each caller attaches the handling its own path needs, and the
+    // read can coalesce onto. The returned promise carries the real outcome.
-    // slot is cleared once the cycle settles.
+    // Each caller attaches the handling its own path needs, and the slot is
-    private startCycle(): Promise<void> {
+    // cleared once the work settles.
-        const cycle = this.refreshCycle();
+    private startCycle(
+        isRefresh: boolean,
+        work: () => Promise<void>,
+    ): Promise<void> {
+        const cycle = work();
         this.cycle = cycle;
+        this.cycleIsRefresh = isRefresh;
         void cycle.then(
             () => {
                 if (this.cycle === cycle) this.cycle = undefined;
@@ -751,9 +815,9 @@ export class Library {
             this.lastError = undefined;
             this.emit({ operation: "refresh", status: "done" });
             // Backfill ML data for the files this refresh knows about. It runs
-            // outside the refresh's success/failure so a fetch or disk problem
+            // outside the refresh's success or failure, so a fetch or disk
-            // there never marks the metadata refresh failed, and it is not
+            // problem there never marks the metadata refresh failed. It is not
-            // awaited so it never stalls the refresh interval. Its failure is
+            // awaited, so it never stalls the refresh interval. Its failure is
             // reported through `status()` and `onProgress`.
             void this.fetchMLDataNow().catch(() => {});
         } catch (err) {
@@ -766,11 +830,14 @@ export class Library {
 
     // Fetch every change since the stored cursor, then commit. All network
     // reads happen before any store mutation, so a fetch that throws leaves the
-    // store untouched and the previous snapshot intact. A collection or file
+    // store untouched and the previous snapshot intact.
-    // that does not decrypt is left out instead, as if deleted, with the reason
+    //
-    // kept in the store: the cursor moves past it, so no later refresh sees it
+    // From a stored cursor of 0, the server lists every live collection. The
-    // again until the server's copy changes.
+    // refresh then replaces all the store holds, and counts every collection
+    // as new. Only `refreshCollection()` can have stored anything before it.
+    // So the store ends as it would had `refreshCollection()` never run.
     private async refreshOnce(): Promise<void> {
+        const replace = this.store.collectionsSinceTime === 0;
         const page = await this.client.collectionsSince({
             sinceTime: this.store.collectionsSinceTime,
         });
@@ -778,16 +845,19 @@ export class Library {
         // Stage per-collection file diffs. A collection's files are
         // re-enumerated only when its updationTime has advanced past the cached
         // copy; an unchanged album's file list cannot have changed. New
-        // collections enumerate from the beginning of time. Each collection
+        // collections enumerate from the beginning of time. When the refresh
+        // replaces the store, every collection counts as new. Each collection
         // whose files are fetched is reported, with how many there are to
         // fetch.
+        const storedCopy = (id: number): Collection | undefined =>
+            replace ? undefined : this.store.getCollection(id);
         const changedCollections = page.collections.filter((collection) => {
-            const known = this.store.getCollection(collection.id);
+            const known = storedCopy(collection.id);
             return !known || collection.updationTime > known.updationTime;
         });
         const filePages: { collectionID: number; page: FilesPage }[] = [];
         for (const collection of changedCollections) {
-            const known = this.store.getCollection(collection.id);
+            const known = storedCopy(collection.id);
             const filePage = await this.client.filesSince({
                 collectionID: collection.id,
                 collectionKey: collection.key,
@@ -802,8 +872,55 @@ export class Library {
             });
         }
 
-        // Network work done; commit to the store and persist only if something
+        await this.commit(page, filePages, replace);
-        // actually changed.
+    }
+
+    // `refreshCollection()`'s work, run in the slot: fetch the files of one
+    // collection changed since the stored copy, then commit. It resolves to
+    // whether the store then holds the collection.
+    private async refreshCollectionOnce(
+        collection: Collection,
+    ): Promise<boolean> {
+        const known = this.store.getCollection(collection.id);
+        // A refresh has received the account's collections, and this one is
+        // not stored. It is new since then, or a refresh dropped it. Leave it
+        // to the next refresh, which adds new collections after the stored
+        // ones, in the server's order.
+        if (!known && this.store.collectionsSinceTime > 0) return false;
+        // The stored copy is as new or newer, so there is nothing to fetch.
+        if (known && collection.updationTime <= known.updationTime) return true;
+        const filePage = await this.client.filesSince({
+            collectionID: collection.id,
+            collectionKey: collection.key,
+            sinceTime: known ? known.updationTime : 0,
+        });
+        // The stored cursor stays where it is, so the next refresh still
+        // fetches the files of every other collection that changed.
+        await this.commit(
+            {
+                collections: [collection],
+                deleted: [],
+                cursor: this.store.collectionsSinceTime,
+            },
+            [{ collectionID: collection.id, page: filePage }],
+            false,
+        );
+        return true;
+    }
+
+    // Commit a collections page and the file pages fetched for its collections
+    // to the store. With `replace`, the page lists every live collection, so
+    // the commit first deletes every stored collection. A collection or file
+    // that does not decrypt is left out, as if deleted. The reason is kept in
+    // the store. No later refresh sees it again until the server's copy
+    // changes. Last, save the store when it holds changes not yet saved.
+    private async commit(
+        page: CollectionsPage,
+        filePages: { collectionID: number; page: FilesPage }[],
+        replace: boolean,
+    ): Promise<void> {
+        // The network work is done, so change the store now. `changed` says
+        // whether this commit changed anything.
         let changed = false;
 
         if (this.store.userID !== this.userID) {
@@ -811,6 +928,13 @@ export class Library {
             changed = true;
         }
 
+        if (replace) {
+            for (const { id } of this.store.listCollections()) {
+                this.store.deleteCollection(id);
+                changed = true;
+            }
+        }
+
         for (const id of page.deleted) {
             if (this.store.getCollection(id)) {
                 this.store.deleteCollection(id);
@@ -864,10 +988,10 @@ export class Library {
         if (changed) this.unsaved = true;
 
         // Reproject and notify subscribers of the delta. This tracks RAM (what
-        // reads see), so it fires whether or not the save below succeeds; a
+        // reads see), so it fires whether or not the save below succeeds. A
-        // save failure surfaces separately through `status().lastError`.
+        // failed save rejects the caller, and a refresh also records it in
-        // `lastRecords` advances every changed refresh so the next diff is
+        // `status().lastError`. `lastRecords` advances on every commit that
-        // against current state.
+        // changes something, so the next diff is against current state.
         if (changed) {
             const next = this.deriveNow();
             if (this.subscribers.size > 0) {
@@ -878,16 +1002,16 @@ export class Library {
             // Recompute the fill orders and pinned set against the new library.
             this.precache?.update(next);
         }
-        // Re-kick the fills every cycle: a finished sweep starts afresh to pick
+        // Re-kick the fills on every commit. A finished sweep starts afresh to
-        // up new files and retry any that failed, and a running one is left be.
+        // pick up new files and retry any that failed. A running one is left
+        // be.
         this.precache?.start();
 
         // Persist whenever RAM holds changes disk has not accepted — including
         // changes an earlier cycle staged whose save failed. `unsaved` clears
-        // only once a save lands, so a save failure both stays visible through
+        // only once a save lands, so a later commit retries a failed save even
-        // `status().lastError` (the throw below records it) and keeps being
+        // when it changes nothing. A failed save rejects the caller, and a
-        // retried, instead of a later empty refresh silently clearing it while
+        // refresh also records it in `status().lastError`.
-        // the on-disk cache is still behind RAM.
         if (this.unsaved) {
             await this.store.save();
             this.unsaved = false;
@@ -903,13 +1027,14 @@ export class Library {
         return this.mlFetch;
     }
 
-    // One ML fetch pass: fetch, decrypt and store the ML data for every file
+    // One ML fetch pass. It fetches, decrypts and stores the ML data of every
-    // the store knows about that is not cached (or whose `updationTime` has
+    // file the store knows about that is not cached, or whose `updationTime`
-    // advanced), through the metadata pool, and update the CLIP index. For a
+    // has advanced. It fetches through the metadata pool, and updates the CLIP
-    // file whose ML data does not decrypt, gunzip or parse, it gathers the
+    // index. For a file whose ML data does not decrypt, gunzip or parse, it
-    // reason instead, and puts the reasons it gathered in `mlDataErrors` when
+    // gathers the reason instead. It puts the reasons it gathered in
-    // it ends without failing. A failure leaves `mlDataErrors` as it was and
+    // `mlDataErrors` when it ends without failing. A failure leaves
-    // is reported through `status()` and `onProgress`, then thrown.
+    // `mlDataErrors` as it was and is reported through `status()` and
+    // `onProgress`, then thrown.
     private async runMLFetch(): Promise<void> {
         const mldata = this.mlStore;
         // Bind so the call keeps the client as its receiver when invoked
@@ -977,9 +1102,9 @@ export class Library {
         }));
     }
 
-    // The distinct files the store holds, one entry per fileID (a file in
+    // The distinct files the store holds, one entry per fileID, since a file
-    // several collections shares its ML data), each carrying the key and the
+    // in several collections shares its ML data. Each entry carries the key
-    // newest `updationTime` seen across its memberships.
+    // and the newest `updationTime` seen across the file's memberships.
     private uniqueFiles(): {
         id: number;
         key: Uint8Array;

src/library/store.ts

@@ -70,12 +70,6 @@ export class MetadataStore {
     userID = 0;
     collectionsSinceTime: Microseconds = 0;
 
-    // True when `load` populated this store from a valid existing file; false
-    // on a first run or a missing/corrupt/wrong-version file that loaded empty.
-    // `Library.open` reads it to decide whether the first refresh may run in
-    // the background (an existing copy already serves reads) or must be awaited.
-    loadedFromDisk = false;
-
     private readonly collections = new Map<number, Collection>();
     private readonly files = new Map<string, EnteFile>();
     private undecryptable: Undecryptable[] = [];
@@ -102,7 +96,6 @@ export class MetadataStore {
             if (parsed.schemaVersion !== METADATA_SCHEMA_VERSION) {
                 return store;
             }
-            store.loadedFromDisk = true;
             store.userID = parsed.userID ?? 0;
             store.collectionsSinceTime = parsed.collectionsSinceTime ?? 0;
             for (const stored of parsed.collections ?? []) {
@@ -229,8 +222,14 @@ export class MetadataStore {
         this.files.delete(fileKey(collectionID, fileID));
     }
 
+    // Sorted by collection ID, then file ID, so the order does not depend on
+    // when each record was fetched.
     listUndecryptable(): Undecryptable[] {
-        return [...this.undecryptable];
+        return [...this.undecryptable].sort(
+            (a, b) =>
+                a.collectionID - b.collectionID ||
+                (a.fileID ?? 0) - (b.fileID ?? 0),
+        );
     }
 
     // Replaces any earlier record of the same collection or file.

test/cli/commands.test.ts

@@ -124,20 +124,35 @@ const FILES: Record<number, EnteFile[]> = {
 // thumbnail as empty. `withNewFile` adds new.jpg (102) to Vacation, advancing
 // the collection's updationTime as the server does. `beachInWork` adds
 // beach.jpg (100) to Work as well, so that one file is in both albums.
-// `refreshError` makes listing collections fail with that message.
+// `newAlbums` adds the albums A (3) and B (4), in that order, which both hold
+// shared.jpg (300). `refreshError` makes listing collections fail with that
+// message.
 const fakeClient = (
     opts: {
         failID?: number;
         emptyThumbID?: number;
         withNewFile?: boolean;
         beachInWork?: boolean;
+        newAlbums?: boolean;
         refreshError?: string;
     } = {},
 ) => {
-    const collections = opts.withNewFile
+    let collections = opts.withNewFile
         ? [{ ...COLLECTIONS[0], updationTime: 2 }, COLLECTIONS[1]]
         : COLLECTIONS;
     let files = FILES;
+    if (opts.newAlbums) {
+        collections = [
+            ...collections,
+            { ...collection(3, "A"), updationTime: 2 },
+            { ...collection(4, "B"), updationTime: 2 },
+        ];
+        files = {
+            ...files,
+            3: [file(300, 3, "shared.jpg")],
+            4: [file(300, 4, "shared.jpg")],
+        };
+    }
     if (opts.withNewFile) {
         files = {
             ...files,
@@ -535,9 +550,7 @@ describe("files", () => {
 
     it("exits 1 for an unknown collection", async () => {
         expect(await filesCommand(context(), "9", {})).toBe(1);
-        expect(stderr.text).toBe(
+        expect(stderr.text).toBe("Collection 9 not found\n");
-            FETCHED_BOTH_ALBUMS + "Collection 9 not found\n",
-        );
     });
 
     // Without a collection ID it lists every file in the account once (issue
@@ -571,6 +584,57 @@ describe("files", () => {
         ]);
         expect(stderr.text).toBe(FETCHED_BOTH_ALBUMS);
     });
+
+    // `files 2` on an empty cache stores Work alone. The refresh that `files`
+    // then waits for must still store Vacation first, as the server lists it.
+    it("without a collection ID lists in the server's order after files 2 on an empty cache", async () => {
+        const ctx = context(fakeClient({ beachInWork: true }));
+        expect(await filesCommand(ctx, "2", {})).toBe(0);
+        stdout.text = "";
+        stderr.text = "";
+
+        expect(await filesCommand(ctx, undefined, { json: true })).toBe(0);
+        expect(
+            JSON.parse(stdout.text).map(
+                (row: { id: number; collectionID: number }) => [
+                    row.id,
+                    row.collectionID,
+                ],
+            ),
+        ).toEqual([
+            [100, 1],
+            [101, 1],
+            [200, 2],
+        ]);
+        expect(stderr.text).toBe(FETCHED_BOTH_ALBUMS);
+    });
+
+    // After a refresh, the server adds A and then B. `files 4` must not store B
+    // ahead of A, so it waits for a refresh, which stores both in that order.
+    it("without a collection ID lists new albums in the server's order after files with the second one's ID", async () => {
+        expect(await filesCommand(context(), undefined, {})).toBe(0);
+        const ctx = context(fakeClient({ newAlbums: true }));
+        stdout.text = "";
+
+        expect(await filesCommand(ctx, "4", {})).toBe(0);
+        expect(stdout.text).toBe("300\timage\tshared.jpg\n");
+        stdout.text = "";
+
+        expect(await filesCommand(ctx, undefined, { json: true })).toBe(0);
+        expect(
+            JSON.parse(stdout.text).map(
+                (row: { id: number; collectionID: number }) => [
+                    row.id,
+                    row.collectionID,
+                ],
+            ),
+        ).toEqual([
+            [100, 1],
+            [101, 1],
+            [200, 2],
+            [300, 3],
+        ]);
+    });
 });
 
 describe("get and get-thumb", () => {
@@ -1394,7 +1458,7 @@ describe("backup-metadata --exif", () => {
 // collection list alone and stores nothing.)
 describe("backup-metadata and the thumbnail helpers refresh first", () => {
     beforeEach(async () => {
-        expect(await filesCommand(context(), "1", {})).toBe(0);
+        expect(await filesCommand(context(), undefined, {})).toBe(0);
         stdout.text = "";
         stderr.text = "";
     });
@@ -1579,11 +1643,13 @@ describe("an ID given on the command line", () => {
 
 // An account with many albums (issue #210). On an empty cache `collections`
 // used to wait for a refresh that fetched and decrypted the files of every
-// album, one album after another, before it printed anything, so on such an
+// album, one album after another. It printed nothing until then, so on such an
-// account it seemed to hang. The account here has 40 albums of one photo each,
+// account it seemed to hang. `files` with an album's ID did the same before it
-// encrypted as Ente's clients encrypt them, on the fake Ente server of
+// listed that album (issue #217). The account here has 40 albums of one photo
-// `test/ente-server.ts`, which also records the path of each request quak
+// each, encrypted as Ente's clients encrypt them. The fake Ente server of
-// sends. The session is the one logging in to that server saves.
+// `test/ente-server.ts` serves them. A wrapper around it records the path and
+// query of each request quak sends. The session is the one logging in to that
+// server saves.
 describe("an account with many albums", () => {
     const ALBUMS = 40;
     const PASSWORD = "many-albums";
@@ -1664,7 +1730,8 @@ describe("an account with many albums", () => {
                     : input instanceof URL
                       ? input.href
                       : input.url;
-            paths.push(new URL(url).pathname);
+            const { pathname, search } = new URL(url);
+            paths.push(pathname + search);
             return ente(input, init);
         }) as typeof globalThis.fetch;
         const client = await Client.login({
@@ -1698,7 +1765,7 @@ describe("an account with many albums", () => {
             albums += `${id}\talbum\tAlbum ${id}\n`;
         expect(stdout.text).toBe(albums);
         expect(stderr.text).toBe("");
-        expect(paths).toEqual(["/collections/v2"]);
+        expect(paths).toEqual(["/collections/v2?sinceTime=0"]);
 
         // It stored nothing that would make a refresh skip an album's files:
         // `files` after it still finds the album's photo.
@@ -1707,33 +1774,59 @@ describe("an account with many albums", () => {
         expect(stdout.text).toBe("700\timage\tphoto-7.jpg\n");
     });
 
-    it("files counts on stderr each album whose files its refresh fetched", async () => {
+    it("files fetches the files of the album it lists and of no other", async () => {
         expect(await filesCommand(accountContext(), "7", {})).toBe(0);
 
         expect(stdout.text).toBe("700\timage\tphoto-7.jpg\n");
+        expect(stderr.text).toBe("");
+        expect(paths).toEqual([
+            "/collections/v2?sinceTime=0",
+            "/collections/v2/diff?collectionID=7&sinceTime=0",
+        ]);
+    });
+
+    // The first listing stored the album, so the second finds its stored copy
+    // current and asks for no album's files.
+    it("files run again for the same album sends no request for its files", async () => {
+        const ctx = accountContext();
+        expect(await filesCommand(ctx, "7", {})).toBe(0);
+        stdout.text = "";
+        paths.length = 0;
+
+        expect(await filesCommand(ctx, "7", {})).toBe(0);
+        expect(stdout.text).toBe("700\timage\tphoto-7.jpg\n");
+        expect(paths).toEqual(["/collections/v2?sinceTime=0"]);
+    });
+
+    it("files with no album's ID counts on stderr each album whose files its refresh fetched", async () => {
+        expect(await filesCommand(accountContext(), undefined, {})).toBe(0);
+
+        let photos = "";
         let progress = "";
         for (let n = 1; n <= ALBUMS; n++) {
+            photos += `${n * 100}\timage\tphoto-${n}.jpg\n`;
             progress += `Fetched the files of ${n} of ${ALBUMS} collections\n`;
         }
+        expect(stdout.text).toBe(photos);
         expect(stderr.text).toBe(progress);
     });
 
     // `--json` shapes stdout only, so the refresh's progress is still counted
     // on stderr.
-    it("files --json counts on stderr each album whose files its refresh fetched", async () => {
+    it("files --json with no album's ID counts on stderr each album whose files its refresh fetched", async () => {
-        expect(await filesCommand(accountContext(), "7", { json: true })).toBe(
+        expect(
-            0,
+            await filesCommand(accountContext(), undefined, { json: true }),
-        );
+        ).toBe(0);
 
-        expect(JSON.parse(stdout.text)).toEqual([
+        const rows = JSON.parse(stdout.text);
-            {
+        expect(rows).toHaveLength(ALBUMS);
-                id: 700,
+        expect(rows[6]).toEqual({
-                title: "photo-7.jpg",
+            id: 700,
-                fileType: "image",
+            title: "photo-7.jpg",
-                creationTime: 1000,
+            fileType: "image",
-                collectionID: 7,
+            creationTime: 1000,
-            },
+            collectionID: 7,
-        ]);
+        });
         let progress = "";
         for (let n = 1; n <= ALBUMS; n++) {
             progress += `Fetched the files of ${n} of ${ALBUMS} collections\n`;

test/cli/read.test.ts

@@ -3,13 +3,17 @@
  * issue #36, issue #52).
  *
  * The `collections`, `files`, `get`, and `get-thumb` commands must answer for
- * current server state, not the local cache. `files`, `get` and `get-thumb`
+ * current server state, not the local cache. `files` without a collection ID,
- * force a `Library.fresh()` round-trip before they read; the stand-in library
+ * `get` and `get-thumb` force a `Library.fresh()` round-trip before they read.
- * below serves nothing until `fresh()` has been awaited, so a helper that read
+ * The stand-in library below serves nothing until `fresh()` has been awaited.
- * without refreshing would come back empty and fail here. `collections` asks
+ * A helper that read without refreshing would come back empty and fail here.
- * the library for the collection list alone (`freshCollections()`, issue
+ * `collections` asks the library for the collection list alone
- * #210), and must not wait for a refresh, which would fetch the files of every
+ * (`freshCollections()`, issue #210). It must not wait for a refresh, which
- * collection.
+ * would fetch the files of every collection. `files COLLECTION` reads that list
+ * too, then brings that one collection up to date (`refreshCollection()`,
+ * issue #217). The stand-in serves a collection's files once `fresh()` or
+ * `refreshCollection()` for that collection has run. When `refreshCollection()`
+ * stores nothing, `files COLLECTION` forces a refresh instead.
  *
  * `collections` and `files` also list in the library's enumeration order
  * (`listCollections`/`listFiles`) — the order the pre-library CLI printed — not
@@ -64,12 +68,17 @@ const file = (
 
 // A library that reveals its records only after `fresh()` has been awaited, and
 // serves them in the enumeration order it was given. `freshCollections()`
-// answers the collection list in that order without a refresh. `photos.byID`
+// answers the collection list in that order without a refresh.
-// returns a stand-in `Photo` carrying just the fileID the helper passes
+// `refreshCollection()` reveals the files of that one collection.
-// through.
+// `photos.byID` returns a stand-in `Photo` carrying just the fileID the helper
+// passes through.
 class FakeLibrary implements FreshReadLibrary {
     freshCalls = 0;
     freshCollectionsCalls = 0;
+    refreshCollectionIDs: number[] = [];
+    // What `refreshCollection()` resolves to. With false it reveals nothing,
+    // as a library that has had a refresh does for a collection it lacks.
+    refreshCollectionHolds = true;
     private refreshed = false;
 
     constructor(
@@ -88,6 +97,11 @@ class FakeLibrary implements FreshReadLibrary {
         return this.collections;
     }
 
+    async refreshCollection(collection: Collection): Promise<boolean> {
+        this.refreshCollectionIDs.push(collection.id);
+        return this.refreshCollectionHolds;
+    }
+
     getCollection(id: number): Collection | undefined {
         if (!this.refreshed) return undefined;
         return this.collections.find((c) => c.id === id);
@@ -98,7 +112,11 @@ class FakeLibrary implements FreshReadLibrary {
     }
 
     listFiles(collectionID: number): EnteFile[] {
-        return this.refreshed
+        const current =
+            this.refreshed ||
+            (this.refreshCollectionHolds &&
+                this.refreshCollectionIDs.includes(collectionID));
+        return current
             ? this.files.filter((f) => f.collectionID === collectionID)
             : [];
     }
@@ -138,18 +156,25 @@ describe("CLI read helpers (issue #36 amendment, issue #52)", () => {
         expect(rows.map((c) => c.id)).not.toEqual(newestFirst);
     });
 
-    it("freshFiles refreshes first, lists in enumeration order, keeps raw fields", async () => {
+    it("freshFiles brings the collection alone up to date, lists in enumeration order, keeps raw fields", async () => {
         // Enumeration order by id 10, 11, 12; creationTimes ascending, so a
-        // newest-first sort would reverse them.
+        // newest-first sort would reverse them. Collection 2's file is not
+        // listed.
         const files = [
             file(10, 1, 1_700_000_000_000_000),
             file(11, 1, 1_700_000_000_000_001),
             file(12, 1, 1_700_000_000_000_002),
+            file(20, 2, 1_700_000_000_000_003),
         ];
-        const lib = new FakeLibrary([collection(1, 100)], files);
+        const lib = new FakeLibrary(
+            [collection(1, 100), collection(2, 100)],
+            files,
+        );
 
         const rows = await freshFiles(lib, 1);
-        expect(lib.freshCalls).toBe(1);
+        expect(lib.freshCollectionsCalls).toBe(1);
+        expect(lib.refreshCollectionIDs).toEqual([1]);
+        expect(lib.freshCalls).toBe(0);
         expect(rows?.map((f) => f.id)).toEqual([10, 11, 12]);
 
         // Field values come from raw metadata: microsecond creationTime and the
@@ -203,10 +228,25 @@ describe("CLI read helpers (issue #36 amendment, issue #52)", () => {
         ]);
     });
 
+    it("freshFiles forces a refresh when refreshCollection stores nothing", async () => {
+        const lib = new FakeLibrary(
+            [collection(1, 100)],
+            [file(10, 1, 1_700_000_000_000_000)],
+        );
+        lib.refreshCollectionHolds = false;
+
+        const rows = await freshFiles(lib, 1);
+        expect(lib.refreshCollectionIDs).toEqual([1]);
+        expect(lib.freshCalls).toBe(1);
+        expect(rows?.map((f) => f.id)).toEqual([10]);
+    });
+
     it("freshFiles returns undefined for an unknown collection", async () => {
         const lib = new FakeLibrary([collection(1, 100)], []);
         const rows = await freshFiles(lib, 999);
-        expect(lib.freshCalls).toBe(1);
+        expect(lib.freshCollectionsCalls).toBe(1);
+        expect(lib.refreshCollectionIDs).toEqual([]);
+        expect(lib.freshCalls).toBe(0);
         expect(rows).toBeUndefined();
     });
 

test/library/fresh.test.ts

@@ -17,6 +17,14 @@
  *  4. `freshCollections()` reads the collection list alone, with one request
  *     and no collection's files, and stores nothing, so the next refresh still
  *     fetches the files of every collection (issue #210).
+ *  5. `refreshCollection()` brings one collection up to date in the store
+ *     (issue #217). It leaves the stored cursor where it was, so the next
+ *     refresh still fetches the files of every other collection that changed.
+ *     It never runs at the same time as a refresh. After a refresh, it stores
+ *     no collection the store does not hold: not a new one, and not one a
+ *     refresh deleted. `close()` waits for it. A library opened on a cache that
+ *     only it wrote awaits its first refresh. That refresh replaces what it
+ *     stored, in the server's order.
  *
  * The client is the same metadata-only mock the background-refresh tests use:
  * no crypto, no network, scripted pages, and a record of each call. A long
@@ -30,6 +38,7 @@ import { tmpdir } from "node:os";
 import { join } from "node:path";
 
 import { Library } from "../../src/library/index.js";
+import { MetadataStore } from "../../src/library/store.js";
 import type { CollectionsPage, FilesPage } from "../../src/client.js";
 import type { Collection, EnteFile } from "../../src/model/types.js";
 
@@ -144,6 +153,26 @@ const openSeeded = async (
     return { client, lib };
 };
 
+// Hold the client's next files request until `release()` is called. `started`
+// resolves once that request has been sent.
+const holdNextFilesRequest = (
+    client: MockClient,
+): { started: Promise<void>; release: () => void } => {
+    let release!: () => void;
+    const held = new Promise<void>((r) => (release = r));
+    let sent!: () => void;
+    const started = new Promise<void>((r) => (sent = r));
+    const realFilesSince = client.filesSince.bind(client);
+    client.filesSince = async (args) => {
+        client.filesSince = realFilesSince;
+        const page = await realFilesSince(args);
+        sent();
+        await held;
+        return page;
+    };
+    return { started, release };
+};
+
 describe("Library.fresh", () => {
     let dir: string;
     let cacheDirectory: string;
@@ -340,3 +369,243 @@ describe("Library.freshCollections", () => {
         }
     });
 });
+
+describe("Library.refreshCollection", () => {
+    let dir: string;
+    let cacheDirectory: string;
+
+    beforeEach(() => {
+        dir = mkdtempSync(join(tmpdir(), "quak-refresh-collection-"));
+        cacheDirectory = join(dir, "cache");
+    });
+
+    afterEach(() => {
+        rmSync(dir, { recursive: true, force: true });
+    });
+
+    // Collections 1 and 2 are stored at updationTime 100, with a stored cursor
+    // of 100, and then both change on the server.
+    it("fetches the files of one changed collection and leaves the others to the next refresh", async () => {
+        const client = new MockClient();
+        client.collectionsQueue.push({
+            collections: [collection(1, 100), collection(2, 100)],
+            deleted: [],
+            cursor: 100,
+        });
+        client.filesFor(1, {
+            files: [file(1001, 1, 90)],
+            deleted: [],
+            cursor: 90,
+        });
+        client.filesFor(2, {
+            files: [file(2001, 2, 90)],
+            deleted: [],
+            cursor: 90,
+        });
+        const lib = await Library.open({
+            client,
+            cacheDirectory,
+            refreshIntervalSeconds: SLOW_INTERVAL,
+        });
+        try {
+            client.filesCalls.length = 0;
+            client.filesFor(1, {
+                files: [file(1002, 1, 110)],
+                deleted: [],
+                cursor: 110,
+            });
+            client.filesFor(2, {
+                files: [file(2002, 2, 120)],
+                deleted: [],
+                cursor: 120,
+            });
+
+            // Collection 1's files alone, since the stored copy.
+            expect(await lib.refreshCollection(collection(1, 110))).toBe(true);
+            expect(client.filesCalls).toEqual([
+                { collectionID: 1, sinceTime: 100 },
+            ]);
+            expect(lib.listFiles(1).map((f) => f.id)).toEqual([1001, 1002]);
+            expect(lib.listFiles(2).map((f) => f.id)).toEqual([2001]);
+
+            // The stored copy is now current, so no request.
+            await lib.refreshCollection(collection(1, 110));
+            expect(client.filesCalls).toHaveLength(1);
+
+            // The next refresh asks from the stored cursor, 100, so it still
+            // sees collection 2 changed and fetches its files.
+            client.collectionsQueue.push({
+                collections: [collection(1, 110), collection(2, 120)],
+                deleted: [],
+                cursor: 120,
+            });
+            await lib.fresh();
+            expect(client.collectionsSinceTimes).toEqual([0, 100]);
+            expect(client.filesCalls).toEqual([
+                { collectionID: 1, sinceTime: 100 },
+                { collectionID: 2, sinceTime: 100 },
+            ]);
+            expect(lib.listFiles(2).map((f) => f.id)).toEqual([2001, 2002]);
+        } finally {
+            await lib.close();
+        }
+    });
+
+    // Collection 1 is stored at 100. `refreshCollection()` asks for it at 110,
+    // which adds file 1002. While that files request waits, a fresh read
+    // starts a refresh. The server tells that refresh that collection 1 was
+    // deleted at 130.
+    it("holds off a refresh that starts during the files request, which then deletes the collection", async () => {
+        const { client, lib } = await openSeeded(cacheDirectory);
+        const files = holdNextFilesRequest(client);
+        try {
+            client.filesFor(1, {
+                files: [file(1002, 1, 110)],
+                deleted: [],
+                cursor: 110,
+            });
+            client.collectionsQueue.push({
+                collections: [],
+                deleted: [1],
+                cursor: 130,
+            });
+
+            const refreshing = lib.refreshCollection(collection(1, 110));
+            await files.started;
+            const reading = lib.fresh();
+            // The refresh has not sent its collections request yet.
+            await new Promise((r) => setImmediate(r));
+            expect(client.collectionsSinceTimes).toEqual([0]);
+
+            files.release();
+            await refreshing;
+            await reading;
+            expect(client.collectionsSinceTimes).toEqual([0, 100]);
+            expect(lib.getCollection(1)).toBeUndefined();
+            expect(lib.listFiles(1)).toEqual([]);
+        } finally {
+            files.release();
+            await lib.close();
+        }
+    });
+
+    // `freshCollections()` lists collection 1 at 110. Before
+    // `refreshCollection()` is called, a refresh learns that it was deleted at
+    // 130.
+    it("stores nothing for a collection that a refresh deleted before the call", async () => {
+        const { client, lib } = await openSeeded(cacheDirectory);
+        try {
+            client.collectionsQueue.push(
+                { collections: [collection(1, 110)], deleted: [], cursor: 110 },
+                { collections: [], deleted: [1], cursor: 130 },
+            );
+            const [listed] = await lib.freshCollections();
+            await lib.fresh();
+            client.filesCalls.length = 0;
+
+            expect(await lib.refreshCollection(listed)).toBe(false);
+            expect(client.filesCalls).toEqual([]);
+            expect(lib.getCollection(1)).toBeUndefined();
+        } finally {
+            await lib.close();
+        }
+    });
+
+    // A refresh has stored collection 1. Collection 2 is new on the server
+    // since then. Only the next refresh may add it, after collection 1.
+    it("stores nothing for a collection that is new since the last refresh", async () => {
+        const { client, lib } = await openSeeded(cacheDirectory);
+        try {
+            client.filesCalls.length = 0;
+
+            expect(await lib.refreshCollection(collection(2, 110))).toBe(false);
+            expect(client.filesCalls).toEqual([]);
+            expect(lib.getCollection(2)).toBeUndefined();
+        } finally {
+            await lib.close();
+        }
+    });
+
+    // The caller may remove the cache directory once `close()` resolves, so
+    // the cache write must have landed by then.
+    it("close() waits for a refreshCollection() in flight", async () => {
+        const { client, lib } = await openSeeded(cacheDirectory);
+        const files = holdNextFilesRequest(client);
+        client.filesFor(1, {
+            files: [file(1002, 1, 110)],
+            deleted: [],
+            cursor: 110,
+        });
+
+        const refreshing = lib.refreshCollection(collection(1, 110));
+        await files.started;
+        let closed = false;
+        const closing = lib.close().then(() => {
+            closed = true;
+        });
+        await new Promise((r) => setImmediate(r));
+        expect(closed).toBe(false);
+
+        files.release();
+        await closing;
+        const saved = await MetadataStore.load(
+            join(cacheDirectory, "metadata.json"),
+        );
+        expect(saved.listFiles(1).map((f) => f.id)).toEqual([1001, 1002]);
+        await refreshing;
+    });
+
+    // `quak files 2` on an empty cache stores collection 2 alone. A library
+    // opened later on that cache must not serve it as the whole account. Its
+    // first refresh replaces what the cache holds, in the server's order.
+    it("open() awaits the first refresh on a cache that only refreshCollection() wrote", async () => {
+        const client = new MockClient();
+        client.filesFor(2, {
+            files: [file(2001, 2, 90)],
+            deleted: [],
+            cursor: 90,
+        });
+        const first = await Library.open({
+            client,
+            cacheDirectory,
+            refreshOnOpen: false,
+            refreshIntervalSeconds: SLOW_INTERVAL,
+        });
+        expect(await first.refreshCollection(collection(2, 100))).toBe(true);
+        await first.close();
+
+        client.collectionsQueue.push({
+            collections: [collection(1, 100), collection(2, 100)],
+            deleted: [],
+            cursor: 100,
+        });
+        client.filesFor(1, {
+            files: [file(1001, 1, 90)],
+            deleted: [],
+            cursor: 90,
+        });
+        client.filesFor(2, {
+            files: [file(2001, 2, 90)],
+            deleted: [],
+            cursor: 90,
+        });
+        client.filesCalls.length = 0;
+        const lib = await Library.open({
+            client,
+            cacheDirectory,
+            refreshIntervalSeconds: SLOW_INTERVAL,
+        });
+        try {
+            expect(lib.status().lastRefreshAt).toBeDefined();
+            expect(lib.listCollections().map((c) => c.id)).toEqual([1, 2]);
+            // It fetches collection 2's files again, from the beginning.
+            expect(client.filesCalls).toEqual([
+                { collectionID: 1, sinceTime: 0 },
+                { collectionID: 2, sinceTime: 0 },
+            ]);
+            expect(lib.listFiles(2).map((f) => f.id)).toEqual([2001]);
+        } finally {
+            await lib.close();
+        }
+    });
+});

test/library/store.test.ts

@@ -266,4 +266,23 @@ describe("MetadataStore", () => {
         expect(store.getFile(12345, 67890)).toBeUndefined();
         expect(store.getFile(55555, 67890)?.key).toEqual(inB.key);
     });
+
+    // A backup reports these in this order. It must not depend on whether a
+    // refresh or `Library.refreshCollection()` fetched each one first.
+    it("lists what did not decrypt by collection ID, then file ID", async () => {
+        const store = await MetadataStore.load(path);
+        store.putUndecryptable({ collectionID: 2, fileID: 7, error: "a" });
+        store.putUndecryptable({ collectionID: 3, error: "b" });
+        store.putUndecryptable({ collectionID: 1, fileID: 9, error: "c" });
+        store.putUndecryptable({ collectionID: 2, fileID: 5, error: "d" });
+
+        expect(
+            store.listUndecryptable().map((r) => [r.collectionID, r.fileID]),
+        ).toEqual([
+            [1, 9],
+            [2, 5],
+            [2, 7],
+            [3, undefined],
+        ]);
+    });
 });